Fiber for fiber cement and resulting product

ABSTRACT

A fiber-cement product which includes a treated cellulose wood pulp fiber. The fiber is treated with fibrillated carboxymethyl cellulose or a carboxyethyl cellulose and poly(diallyldimethylammonium chloride). The fiber can be bleached or partially bleached, refined or unrefined or a mixture of refined and unrefined fiber.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/495,692, filed on Jun. 13, 2012, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/050,528, filed on Jun. 30,2011.

TECHNICAL FIELD

This relates to fibers for use in fiber cement products and theresulting fiber cement products.

BACKGROUND

The internal structures of houses and other buildings are commonlyprotected from environmental elements by exterior siding, roofing andtrim materials. These siding, roofing and trim materials are typicallyplanks, panels or shingles composed of wood, concrete, brick, aluminum,stucco, wood composites, or fiber-cement composites. Some commonfiber-cement composites are fiber-cement siding, roofing, and trim whichare generally composed of cement and unbleached wood pulp, and,optionally, silica sand, synthetic fibers and various additives.Fiber-cement products offer several advantages over other types ofmaterials, such as wood siding, roofing and trim because fiber-cementproducts are weatherproof, relatively inexpensive to manufacture,fire-resistant, and invulnerable to rotting or insect damage.

Most commercial fiber-reinforced cement siding products are made usingthe Hatschek process. The Hatschek process was initially developed forthe production of asbestos cement composites, but is now also used forthe manufacture of non-asbestos, synthetic and cellulose fiberreinforced cement composites. Non-asbestos, air-cured fiber cementproducts require synthetic fibers as reinforcing fibers and refinedcellulose or equivalent fibers as filtration fibers. Synthetic fibersalone cannot perform the filtration function and therefore require theaddition of cellulose fibers for this purpose.

In the Hatschek process, bales of bleached or unbleached cellulose pulpfibers are re-pulped in water to provide substantially singulatedfibers. The re-pulped fibers are refined and then mixed with cement andadditives such as calcite, and optionally synthetic fibers, silica sand,clay, and other additives to form a mixture. The type of additive willdepend, in part, on the type of curing that will be used. An air-cure ornatural curing process will often use calcite, calcium carbonate, as anadditive and synthetic fibers like polyvinyl alcohol (PVA) fibers asreinforcing fibers. An autoclave curing process will usually use silicasand as an additive.

A thin layer of fiber-cement mixture is deposited on a felt bandsubstrate and vacuum dewatered. This process is repeated until a numberof layers are formed to obtain the final thickness and to provide alayered product. Depending on the desired product and specification theproduct may then be pressed. The product is then cured to form a fiberreinforced cement matrix in sheet form. The curing may be accomplishedby air drying or natural curing in a humid environment, or throughautoclaving. A natural curing process may take 21 to 28 days. It can beaccelerated by the addition of a high humidity environment at elevatedtemperature not higher than 80° C. The material may be used for siding,roofing or trim. The siding form may have the appearance of standardbeveled wood siding. The roofing form may have the appearance ofstandard roofing materials such as shingles, tile, slate or fullprofiled sheets.

In the original Hatschek process asbestos fibers were the fibers ofchoice. In natural curing, asbestos fibers acted as both a reinforcingfiber and as the filtration fiber. A filtration fiber acts as a filtermedium in the cement mixture slurry during the drainage process on theforming or sieve wire (also known as sieve cylinder) to help retaincement and additive particles while the excess water is being removedfrom the cement suspension. If there is no filter medium then a greatdeal of the solids from the slurry will be lost with the water duringthe drainage process. The purpose of the filter medium is to retain thecement mixture within the product while removing the water. The cementmixture will form around and attach to the fibers during the drainageprocess. Filtration fibers aid drainage by trapping particles of cementand other ingredients in the cement mix without greatly slowing down theformation process on the wire.

The fiber cement board manufacturers target high strength combined withgood flexibility in the cement board. These properties are usuallymeasured by a 3-Point Flexure test (similar to ASTM C-1185). Strength isindicated by the modulus of rupture (MOR) of the board. Flexibility isshown by the deflection of the board at maximum load. Maximum load isthe amount of force that can be applied to the board before it breaks.Deflection at maximum load is how far the board deflects from thehorizontal plane of the board before breaking in 3-Point bending. Thesemeasurements are illustrated in FIG. 1.

The asbestos fibers primary function was to reinforce the compositewhile aiding in the filtration process during manufacture of the board.Health and safety issues are eliminating asbestos fibers from use infiber cement manufacture. Synthetic fibers, such as polyvinyl alcohol(PVA) fibers have replaced asbestos fibers. Synthetic fibers, however,do not act as filtration fibers. Synthetic fibers do not deter orprevent the cementitious material from passing through the wire with thewater. Consequently, highly beaten and highly fibrillated, usuallyunbleached, cellulose fiber has been combined with synthetic fiber toprovide filtration capability.

For naturally cured fiber cement board, PVA reinforcement fibers incombination with highly refined cellulose fibers have been used in placeof asbestos fibers. PVA fibers may be used to improve the toughness(calculated by dividing the energy to break by the volume of the boardin 3-Point bending test) of the cement product. The PVA fibers provideacceptable modulus of rupture, maximum load and deflection at maximumload. The highly refined cellulose fibers provide filtration. A typicalfiber amount is 4 to 5% by weight refined cellulose wood pulp fibers and1.5 to 3% by weight PVA fibers. The weight percent is based on the dryweight of the ingredients for the cement product, including the fiber,and indicates the amount of fiber in the cement mix.

The replacement of asbestos fibers with highly beaten cellulose fibersas the filtration fiber may require the use of flocculants as one of theadditives. The natural affinity of cellulose fibers for the mineralsused in fiber cement manufacture is much lower than asbestos. Therefore,flocculants are required for mineral retention, dewatering, formationand machine efficiency. Flocculent selection and optimizationformulations are considered to be a competitive advantage by fibercement manufacturers and kept by each as a trade secret. The typicalflocculants are anionic polyacrylamides or phenol-formaldehyde resin andpoly(ethylene oxide).

Other commonly used fiber cement manufacturing processes known to thoseskilled in the art and which use PVA fibers are: the Magnani process,extrusion, injection molding, hand lay-up, molding and the Mazza pipeprocess.

A drawback to the use of PVA fibers is the high cost of the fibers andthe potential lack of availability of the fiber, as well as theirinability to filter the slurry in the process causing major solids lossif filtration fibers such as highly refined cellulose fibers were notused in combination with the PVA fibers.

Other fibers must be comparable with PVA/wood pulp fiber mixes in termsof toughness, modulus of rupture, maximum load and deflection at maximumload, and filtration, if they are to be considered for use in fibercement board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are photomicrographs of a sample of fibrillated carboxymethylcellulose at magnifications of 100 times, 1000 times and 10,000 timesrespectively.

FIGS. 4-6 are photomicrographs of another sample of fibrillatedcarboxymethyl cellulose at magnifications of 100 times, 1000 times and10,000 times respectively.

FIG. 7 is a representation of one unit of a cellulose molecule.

FIG. 8 is a representation of one unit of a carboxymethyl cellulosemolecule.

FIG. 9 is a representation of one unit of a carboxyethyl cellulosemolecule.

FIG. 10 is a graph showing the modulus of rigidity for several samples.

FIG. 11 is a graph showing the mass specific peak toughness of severalsamples.

FIG. 12 is a graph showing the mass specific total toughness of severalsamples.

DETAILED DESCRIPTION

It was found that poly(diallyldimethyl ammonium chloride) (“polyDADMAC”)polymer can be tightly bound on the surface of cellulose fibers when thefibers are first treated with a low DS (degree ofsubstitution=0.05-0.45) fibrillated carboxyalkyl cellulose dispersion.The degree of substitution is the average number of moles of hydroxylgroups in the cellulose polymer that are transformed to provide thecellulose derivative. The carboxyalkyl cellulose may be carboxymethylcellulose (CMC) or carboxyethyl cellulose. Carboxymethyl cellulose withDS less than about 0.45 is not soluble in water and can be fibrillatedby high shear blending in water. Carboxyethyl cellulose with a DS lessthan about 0.45 is not soluble in water and can be fibrillated by highshear blending in water.

The fibrillated carboxyalkyl cellulose is made by applying a high shearforce on carboxyalkyl cellulose fibers having a DS of 0.01 to 0.45 inwater to pull apart the carboxyalkyl cellulose fibers into fibrillatedmaterial. The energy applied and the method of fibrillation determinesthe level of fibrillation. Low energy fibrillation of low DScarboxyalkyl cellulose fibers first form fragmented sheets or otheraggregates of nano and micro fibrils. High energy fibrillation formssingulated nano and micro fibrils. Singulated nano or micro fibrils orfragmented sheets or other aggregates of entangled nano or micro fibrils(hereafter also called elements) are suitable for treatment of cellulosefibers to modify the cellulose fiber surface for strong binding ofpolyDADMAC polymer. The fibrillated carboxyalkyl cellulose having a DSof 0.01 to 0.45 may have one or more of these elements. The elements mayalso be attached to each other.

The nano and micro size refers to the width of the fibril. Nano fibrilsby definition are below 100 nm in width. Micro fibrils range from 100 nmto 4000 nm in width. The carboxyalkyl material is pulled apart intofibrils having a high aspect ratio of width to length. The fibrils canbe interconnected to form a web-like material. Typical fibrillated lowDS carboxymethyl cellulose is shown in FIGS. 1-6.

Low DS carboxyalkyl cellulose is fibrillated using high shear mixing inwater. Hydropulper, homogenizer, microfuidizer or other high shearfibrillating equipment are suitable for fibrillating low DS carboxyalkylcellulose. Cellulose fiber is then slurried in water and mixed withfibrillated low DS carboxyalkyl cellulose 0.1% to 10% by weight ofcellulose fibers for 1 minute to 2 hours at a temperature of 20 to 80°C. Poly(diallyldimethyl ammonium chloride) (“polyDADMAC”) polymer, 0.1to 10% by weight of cellulose fibers, is then mixed with cellulosefibers treated with fibrillated low DS carboxyalkyl cellulose for 1minute to 2 hours at a temperature of 20 to 80° C.

PolyDADMAC polymer is tightly bound on the fibrillated low DScarboxyalkyl cellulose treated cellulose fibers and the extractabilityof the quaternary ammonium polymer by the alkaline medium of the cementmatrix is very low. Refined and non refined cellulose fibers treated inthis manner when used with synthetic polymers such as polypropylenefibers improves the durability of cellulose fibers in naturally curedfiber cement boards as indicated by durable toughness after acceleratedweathering cycles. Other suitable quaternary ammonium polymers may alsobe used in place of polyDADMAC polymer. Not limiting to any singlemechanism, one possible mechanism is the inhibition of calcificationwithin the cellulose fibers by the anion exchange ability of thequaternary ammonium polymer tightly bound on the surface of cellulosefibers.

The samples shown in Table 1 were tested for modulus of rigidity, massspecific peak toughness and mass specific total toughness.

TABLE 1 Sample Definition Reinforcing Fibers Filtration Fibers PVA PPCFTH FF FFT Cement CaCO3 Sample wt % wt % wt % wt % wt % wt % wt % S13.0% 4.0% 77.0% 16.0% S1R 3.0% 4.0% 77.0% 16.0% S2 4.0% 80.0% 16.0% S2T4.0% 80.0% 16.0% S3 1.5% 4.0% 78.5% 16.0% S3T 1.5% 4.0% 78.5% 16.0% S41.5% 4.0% 2.0% 76.5% 16.0% S4T 1.5% 4.0% 2.0% 76.5% 16.0% S5 1.5% 3.0%1.0% 78.5% 16.0% S5T 1.5% 3.0% 2.0% 77.5% 16.0% S6 1.5% 4.0% 1.0% 77.5%16.0% ST6 1.5% 4.0% 1.0% 77.5% 16.0% PVA = Synthetic unrefined fiber PP= Synthetic unrefined fiber CFTH = Treated, unrefined, unbleachedcellulose fiber FF = Untreated, refined (150 CSF), unbleached cellulosefiber FFT = Treated, refined (150 CSF), unbleached cellulose fiberCement = Cement CaCO3 = Calcium carbonate (used as a filler) Samplesmade with treated filtration fibers are marked with letter T after thenumber. A sample with the duplicated formulation is marked with letter Rafter the number.

Traditionally, refined fibers (150 CSF) are used for filtration purposeto drain the process water rapidly and retain other fibers and cement inthe mix during manufacturing of the fiber cement board. They do notsignificantly contribute in strength and toughness of the board.However, we noticed significant improvement in strength and toughness ofthe board when filtration fibers were treated (samples S4 and S6).

Unrefined cellulose fibers can partially replace costly syntheticfibers. However, to retain the strength and toughness of a board over alonger period of time, it is best to treat these cellulose fibers withthe previously described treatment. With added contribution from treatedrefined fibers, the sample S4T had results comparable to the S1 boardsmade with expensive PVA (synthetic) fibers after ageing. Also, samplesS3 through S6 had used less expensive polypropylene fibers in half theamount of PVA fibers used in the sample S1.

In addition, samples S4 through S6 used half the amount of refinedfiltration fibers. The similar filtration performance noted may be dueto some filtration contribution provided by unrefined cellulose fibers.

At the fiber levels commonly used in the naturally cured fiber cementboard industry, the disclosed treatment of unrefined, unbleached,cellulose fibers resulted in unique fiber that boosts performance ofsynthetic reinforcing fibers and provides some improvement in filtrationcapability. Similarly, the treatment of refined, unbleached, cellulosefibers has resulted in unique, quality filtration fiber that boostsperformance of unrefined fibers in their reinforcing function.

Bleached cellulose wood pulp fibers typically have a carboxyl content of5 or below milliequivalents per 100 g of cellulose fiber (meq/100 g).Cellulose fibers are treated with the fibrillated carboxyalkyl cellulosefibers to provide additional anionic carboxyalkyl groups on the surfaceof the cellulose wood pulp fiber. In one embodiment the cellulose woodpulp fiber has a total carboxyalkyl content of 10 to 40 meq/100 g. Inanother embodiment the cellulose wood pulp fiber has a totalcarboxyalkyl content of 10 to 30 meq/100 g. In another embodiment thecellulose wood pulp fiber has a total carboxyalkyl content of 10 to 20meq/100 g.

It is also possible to have cellulose fibers carboxalkylated to a DS ofabout 0.01 to 0.08 and use such fibers without fibrillation to tightlybind polyDADMAC polymer or another suitable polymeric quaternaryammonium polymer to the fiber surface. This type of modified cellulosefibers refined and non-refined also can provide durable toughness tonaturally cured fiber cement boards when used with synthetic fiber suchas polypropylene fibers.

It is possible to have cellulose fibers catalytically oxidized to obtaina low carboxyl level of below 30 meq/100 g of the fibers and use fiberswithout fibrillation to tightly bind polyDADMAC polymer or anothersuitable polymeric quaternary ammonium polymer to the fiber surface.This type of modified cellulose fibers refined and non-refined also canprovide durable toughness to naturally cured fiber cement boards whenused with synthetic fibers such as polypropylene fibers.

Cellulose is a carbohydrate consisting of a long chain of glucose units,all β-linked through the 1-4 positions. Native plant cellulose moleculesmay have upwards of 2200 of the anhydroglucose units shown in FIG. 7.The number of units is normally referred to as degree of polymerization,or simply D.P. Some loss of D.P. occurs during purification of thecellulose, as in using a chemical pulping process to pulp the wood toobtain the cellulose and separate it from the lignin and some of thehemicellulose in the wood. The D.P. of the final pulp will depend uponthe pulping process used and the test to determine the D.P.

The structure of one unit of cellulose is shown in FIG. 7 and thestructures of one unit of carboxymethyl cellulose and carboxyethylcellulose are shown in FIGS. 8 and 9. The numbers 1-6 on these diagramsare the location of carbon atoms. The carboxyalkyl cellulose may also beattached to the oxygen attached to positions 2 and/or 3 as well asposition 6 or instead of position 6. Carboxyalkyl cellulose is known andthe methods of making it are known.

Every ahydroglucose unit of the cellulose molecule chain is notcarboxylated. The carboxyalkyl content of the derivatized cellulosemolecules present will be determined by the carboxyalkyl content of thecarboxyalkyl cellulose fibers. The degree of substitution is the averagenumber of moles of hydroxyl groups in the cellulose polymer that reactto form the cellulose derivative.

The carboxyalkylated cellulose wood pulp fiber does not have side chainsattached to the cellulose molecule through the carboxyl group.

Water insoluble low DS carboxyalkyl cellulose elements bind to thesurface of cellulose fibers increasing the surface carboxyl level byabout 3-25 meq/100 g. The increased carboxyl level (anionic charge) onthe surface of cellulose fibers increases the level of tightly boundquaternary ammonium polymer (polyDADMAC or other suitable polymericquaternary ammonium polymer) retained on the cellulose fibers andprovides a modified cellulose fiber than can provide durable toughnessin naturally cured fiber cement boards. The treated fibers are also lesshydrophilic than untreated fibers. During fiber cement board making,these fibers increase the filtration speed of the fiber/cement slurrywhile retaining more solids in the formed fiber cement boards. Bothrefined and non-refined treated cellulose fibers have these advantageouscharacteristics. These treated fibers can be used with synthetic fiberssuch as polypropylene fibers and polyvinyl alcohol fibers in fibercement boards advantageously providing durable toughness in thenaturally cured fiber cement boards.

Polymeric quaternary ammonium polymers such as polyDADMAC can be tightlybound on cellulose fiber surface treated with fibrillated low DScarboxyalkyl cellulose elements. PolyDADMAC tightly bound on the surfaceof cellulose fibers using fibrillated low DS carboxyalkyl celluloseelements can behave as an anion exchanging surface that can be initiallyconverted to the hydroxide form by calcium hydroxide (alkaline basepresent in the fiber cement slurry). This process can convert polyDADMACbound on the surface of cellulose fibers to poly(diallyldimethylammonium hydroxide) and calcium chloride during the board formingprocess. Water soluble salts such as calcium chloride will be removedfrom the wet boards during the dewatering process.

Once the fiber cement boards are dried they are subjected to acceleratedaging in testing chambers or undergo aging in natural wet/dry cycles.The calcium hydroxide present in the matrix as particles (low solubilityat 20° C.=0.173 g/100 mL) is gradually depleted by its reaction withdissolved atmospheric carbon dioxide that enters the fiber cement matrixvia the exposed surfaces of the board under wet conditions. Thisreaction forms deposits of calcium carbonate in the cement matrix.Calcium carbonate has very low solubility in water (solubility at 25°C.=0.0015 g/100 mL).

When poly(diallyldimethyl ammonium hydroxide) tightly bound to thesurface of cellulose fibers via fibrillated low DS carboxyalkylcellulose elements is exposed to dissolved atmospheric carbon dioxide,another ion exchange can take place resulting in the formation ofpoly(diallyldimethyl ammonium bicarbonate).

Dissolved calcium hydroxide migrating to the treated cellulose fibersurface can then convert carbonate or bicarbonate form of the quaternaryammonium polymer to the hydroxide form and deposit calcium carbonate atthe fiber/matrix interface. Until all the calcium hydroxide particlespresent in the matrix are depleted, these particles will graduallydissolve in water present in the matrix (rate depends on moisturecontent and prevailing temperature in the matrix due to seasonalvariations) and will react with dissolved atmospheric carbon dioxidemigrating in to the cement board. Most calcium carbonate deposits willform in the cement matrix away from the fibers. When calcium hydroxidepresent in the cement matrix is depleted after many years of weatheringfurther formation of calcium carbonate is not possible.

This postulated mechanism can prevent calcium carbonate deposits beingformed in the lumen or in the surface pores of cellulose fiberssequentially treated with low DS carboxyalkyl elements and a quaternaryammonium polymer. This anion exchange mechanism can prevent or decreasethe tendency of cellulose fibers becoming brittle in the fiber cementboards.

The cellulose wood pulp fibers can be refined or unrefined. Acombination of refined cellulose fibers and unrefined cellulose fiberstreated with fibrillated low DS carboxyalkyl elements and a quaternaryammonium polymer when used with synthetic fibers such as poly propylenefibers can surprisingly improve durable toughness in the naturally curedfiber cement boards.

Experiment 1

Surface Treatment of Unbleached Cellulose Fibers.

Cellulose Fibers Treated in Water

1. with fibrillated CMC fibers (0.45 DS) (4% of cellulose fiber weight)and then

2. with polyDADMAC (100,000-200,000 Mw) (2.4% of cellulose fiberweight).

4.0 g (oven dry basis) of CMC (DS=0.45) were added to 1500 millileters(ml) de-ionized (DI) water in a 3000 ml stainless steel beaker. Themixing resulted in the fibrillation of the CMC. The stainless steelbeaker was placed in a constant temperature water bath and mixing wascontinued using an overhead air mixer. The mixture was mixed for onehour at 80° C.

100 g oven dry (OD) ML1 unbleached cellulose wood pulp fibers in 400 mlDI water were added to the stainless steel beaker and mixed for 30minutes. The temperature was maintained at 80° C. during the mixing.

12.0 g of a 20% stock solution of polyDADMAC purchased fromSigma-Aldrich (2.4 g polyDADMAC) was diluted with 500 ml of DI water andadded to the stainless steel beaker and mixed with the fiber and CMC.After one hour mixing at 80° C., the fibers were filtered using aBuchner funnel/flask under water pump vacuum. The polyDADMAC on thefibers was determined to be 1.76% by Kjeldahl method of nitrogendetermination. The elemental nitrogen content of the fiber is determinedby digesting a small fiber sample in concentrated sulfuric acid. Thisnumber can be converted to the polyDADMAC % on fibers by using the %nitrogen in the elemental composition of polyDADMAC.

5.0 g of the treated wet pulp fibers was added to 5000 ml DI water andmixed for 30 minutes with overhead mixing. The fibers were filteredusing a Buchner funnel/flask under water pump vacuum and the amount ofpolyDADMAC on the cellulose fibers was determined to be 1.38% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

Another 5.0 g of the treated wet pulp fibers was added to 5000 ml of anNaOH solution (pH=12) and mixed for 30 minutes with overhead mixing. Thefibers were filtered using a Buchner funnel/flask under water pumpvacuum and the amount of polyDADMAC on the cellulose fibers wasdetermined to be 1.61% of the weight of the cellulose fibers by Kjeldahlmethod of nitrogen determination.

Experiment 2

Surface Treatment of Unbleached Cellulose Fibers.

Cellulose Fibers Treated in Water

1. with fibrillated CMC fibers (0.45 DS) (4% of cellulose fiber weight)and then

2. with polyDADMAC (100,000-200,000 Mw) (1.2% of cellulose fiberweight).

4.0 g (oven dry basis) of CMC (DS=0.45) was added to 1500 ml DI water ina 3000 ml stainless steel beaker. The stainless steel beaker was placedin a constant temperature water bath and mixing continued using anoverhead air mixer. The CMC dispersion is heated to and maintained at80° C. in the water bath and mixing continued for one hour.

100 g oven dry (OD) ML1 unbleached cellulose wood pulp fibers in 400 mlDI water were added to the stainless steel beaker and mixed for 30minutes. The temperature was maintained at 80° C.

6.0 g of 20% stock solution polyDADMAC purchased from Sigma-Aldrich (1.2g polyDADMAC) was diluted with 500 ml of DI water and added to thebeaker. After mixing for one hour at 80° C., the fibers were filteredusing a Buchner funnel/flask under water pump vacuum. The amount ofpolyDADMAC on the cellulose fibers was determined to be 0.77% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

5.0 g of the treated wet pulp fibers was added to 5000 ml DI water andmixed for 30 minutes using overhead mixing. The fibers were filteredusing a Buchner funnel/flask under water pump vacuum and the amount ofpolyDADMAC on the cellulose fibers was determined to be 0.50% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

Another 5.0 g of the treated wet pulp fibers was added to 5000 ml of aNaOH solution (pH=12) and mixed for 30 minutes using overhead mixing.The fibers were filtered using a Buchner funnel/flask under water pumpvacuum and the amount of polyDADMAC on the cellulose fibers wasdetermined to be 0.50% of the weight of the cellulose fibers by Kjeldahlmethod of nitrogen determination.

Experiment 3

Surface Treatment of Unbleached Cellulose Fibers.

Cellulose Fibers Treated in Water

1. With fibrillated CMC fibers (0.45 DS) (2% of cellulose fiber weight)and then

2. with polyDADMAC (100,000-200,000 Mw) (1.2% of cellulose fiberweight).

2.0 g (oven dry basis) of CMC (DS=0.45) was added to 1500 ml de-ionizedwater in a 3000 ml stainless steel beaker. The stainless steel beakerwas placed in a constant temperature water bath and mixed using anoverhead air mixer. The CMC dispersion was heated to and maintained at80° C. in the water bath. Mixing was for one hour.

Then 100 g OD ML1 cellulose wood pulp fiber in 400 ml DI water was addedto the stainless steel beaker and mixed for 30 minutes. The temperaturewas maintained at 80° C.

Then 6.0 g of 20% stock solution polyDADMAC purchased from Sigma-Aldrich(1.2 g polyDADMAC) diluted with 500 ml of DI water was added to thebeaker and mixed for one hour. The temperature was maintained at 80° C.The fibers were filtered using a Buchner funnel/flask under water pumpvacuum. The amount of polyDADMAC on the cellulose fibers was determinedto be 0.68% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

5.0 g of the treated wet pulp fibers was added to 5000 ml DI water andmixed for 30 minutes using an overhead mixing. The fibers were filtered.The amount of polyDADMAC on the cellulose fibers was determined to be0.58% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

Another 5.0 g of treated wet pulp fibers was added to 5000 ml of an NaOHsolution (pH=12) and mixed for 30 minutes using overhead mixing. Thefibers were filtered using a Buchner funnel/flask under water pumpvacuum. The amount of polyDADMAC on the cellulose fibers was determinedto be 0.54% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

Experiment 4

Surface Treatment of Unbleached Cellulose Fibers.

Cellulose Fibers Treated in Water

1. with fibrillated CMC fibers (0.45 DS) (2% of cellulose fiber weight)and then

2. with polyDADMAC (100,000-200,000 Mw) (3.0% of cellulose fiberweight).

2.0 g (oven dry basis) of CMC (DS=0.45) was added to 1500 ml de-ionizedwater in a 3000 ml stainless steel beaker and mixed using an overheadair mixer. The stainless steel beaker was placed in a constanttemperature water bath and mixing was continued. The CMC dispersion washeated to and maintained at a temperature of 80° C. in the water bath.The mixing was for one hour.

Then 100 g oven dry (OD) ML1 unbleached cellulose wood pulp fibers in400 ml DI water was added to the stainless steel beaker and mixed for 30minutes. The temperature was maintained at 80° C. during the mixing.

Then 15.0 g of 20% stock solution of polyDADMAC (3.0 g polyDADMAC)purchased from Sigma-Aldrich in 500 ml of DI water was added to thebeaker and mixed for one hour. The temperature was maintained at 80° C.The fibers were filtered using a Buchner funnel/flask under water pumpvacuum. The amount of polyDADMAC on the cellulose fibers was determinedto be 1.15% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

5.0 g of the treated wet pulp fibers was added to 5000 ml DI water andmixed for 30 minutes using overhead mixing. The fibers were filteredusing a Buchner funnel/flask under water pump vacuum. The amount ofpolyDADMAC on the cellulose fibers was determined to be 0.86% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

Another 5.0 g of the treated wet pulp fibers was added to 5000 ml NaOHsolution (pH=12) and mixed for 30 minutes using overhead mixing. Thefibers were filtered using a Buchner funnel/flask under water pumpvacuum. The amount of polyDADMAC on the cellulose fibers was determinedto be 1.08% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

Experiment 5

Surface Treatment of Unbleached Cellulose Fibers.

Cellulose Fibers Treated in Water

1. with fibrillated CMC fibers (0.45 DS) (2% of cellulose fiber weight)and then

2. with polyDADMAC (100,000-200,000 Mw) (2.4% of cellulose fiberweight).

2.0 g (oven dry basis) of CMC was added to 1500 ml de-ionized water in a3000 ml stainless steel beaker. The stainless steel beaker was placed ina constant temperature water bath and the CMC was mixed using anoverhead air mixer. The CMC dispersion was heated to and maintained at80° C. in the water bath. Mixing was for one hour.

Then 100 g OD ML1 unbleached cellulose wood pulp fibers in 400 ml DIwater was added to the stainless steel beaker and mixed for 30 minutes.Temperature during mixing was maintained at 80° C.

Then 12.0 g of 20% stock solution polyDADMAC (2.4 g polyDADMAC)purchased from Sigma-Aldrich diluted with 500 ml of DI water was addedto the beaker and mixed for one hour. The temperature during mixing wasmaintained at 80° C. The fibers were filtered using a Buchnerfunnel/flask under water pump vacuum. The amount of polyDADMAC on thecellulose fibers was determined to be 1.15% of the weight of thecellulose fibers by Kjeldahl method of nitrogen determination.

5.0 g of the treated wet pulp fibers was added to 5000 ml DI water andmixed for 30 minutes using overhead mixing. The fibers were filteredusing a Buchner funnel/flask under water pump vacuum. The amount ofpolyDADMAC on the cellulose fibers was determined to be 0.87% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

Another 5.0 g of the treated wet pulp fibers was added in 5000 ml NaOHsolution (pH=12) and mixed for 30 minutes using overhead mixing. Thefibers were filtered using a Buchner funnel/flask under water pumpvacuum. The amount of polyDADMAC on the cellulose fibers was determinedto be 1.04% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

Experiment 6

Surface Treatment of Unbleached Cellulose Fibers.

Cellulose Fibers Treated in Water

1. with fibrillated CMC fibers (0.45 DS) (1% of cellulose fiber weight)and then 2. with polyDADMAC (100,000-200,000 Mw) (3.0% of cellulosefiber weight).

1.0 g (oven dry basis) CMC (DS=0.45) was added to 1500 ml de-ionizedwater in a 3000 ml stainless steel beaker. The stainless steel beakerwas placed in a constant temperature water bath and the CMC dispersionwas mixed using an overhead air mixer. The CMC dispersion was heated toand maintained at a temperature of 80° C. in the water bath. Mixing wasfor one hour.

Then 100 g OD ML1 unbleached cellulose wood pulp fibers in 400 ml DIwater was added to the stainless steel beaker and mixed for 30 minutes.The temperature was maintained at 80° C.

Then 15.0 g of 20% stock solution polyDADMAC (3.0 g polyDADMAC)purchased from Sigma-Aldrich diluted with 500 ml of DI water was addedto the beaker and mixed for one hour. The temperature was maintained at80° C. during mixing. The fibers were filtered using a Buchnerfunnel/flask under water pump vacuum. The amount of polyDADMAC on thecellulose fibers was determined to be 1.10% of the weight of thecellulose fibers by Kjeldahl method of nitrogen determination.

5.0 g of the treated wet pulp fibers was added to 5000 ml DI water andmixed for 30 minutes using overhead mixing. The fibers were filteredusing a Buchner funnel/flask under water pump vacuum. The amount ofpolyDADMAC on the cellulose fibers was determined to be 0.76% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

Another 5.0 g of the treated wet pulp fibers was added to 5000 ml of anNaOH solution (pH=12) and mixed for 30 minutes using overhead mixing.The fibers were filtered using a Buchner funnel/flask under water pumpvacuum. The amount of polyDADMAC on the cellulose fibers was determinedto be 0.95% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

Experiment 7

Surface Treatment of Unbleached Cellulose Fibers.

Cellulose Fibers Treated in Water

1. with fibrillated CMC fibers (0.45 DS) (1% of cellulose fiber weight)and then

2. with Poly DADMAC (100,000-200,000 Mw) (2.4% of cellulose fiberweight).

1.0 g (oven dry basis) of CMC (DS=0.45) was added to 1500 ml de-ionizedwater in a 3000 ml stainless steel beaker. The stainless steel beakerwas placed in a constant temperature water bath and the CMC and waterwere mixed using an overhead air mixer. The CMC dispersion was heated toand maintained at a temperature of 80° C. in the water bath. Mixing wasfor one hour.

Then 100 g OD ML1 unbleached cellulose wood pulp fibers in 400 ml DIwater was added to the stainless steel beaker and mixed for 30 minutes.The temperature was maintained at 80° C.

Then 12.0 g of 20% stock solution polyDADMAC (2.4 g polyDADMAC)purchased from Sigma-Aldrich diluted with 500 ml of DI water was addedto the beaker and mixed with the other ingredients. Mixing was for onehour. Mixing was at 80° C. The fibers were filtered using a Buchnerfunnel/flask under water pump vacuum. The amount of polyDADMAC on thecellulose fibers was determined to be 0.98% of the weight of thecellulose fibers by Kjeldahl method of nitrogen determination.

5.0 g of the treated wet pulp fibers were added to 5000 ml DI water andmixed for 30 minutes using overhead mixing. The fibers were filteredusing a Buchner funnel/flask under water pump vacuum. The amount ofpolyDADMAC on the cellulose fibers was determined to be 0.76% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

Another 5.0 g of the treated wet pulp fibers was added to 5000 ml NaOHsolution (pH=12) and mixed for 30 minutes using overhead mixing. Thefibers were filtered using a Buchner funnel/flask under water pumpvacuum. The amount of polyDADMAC on the cellulose fibers was determinedto be 0.88% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

Experiment 8

Surface Treatment of Unbleached Refined Cellulose Fibers (CSF=150).

Cellulose Fibers Treated in Water

1. with fibrillated CMC fibers (0.45 DS) (4% of cellulose fiber weight)and then

2. with polyDADMAC (100,000-200,000 Mw) (2.4% of cellulose fiberweight).

4.0 g (oven dry basis) of CMC (DS=0.45) was added to 1500 ml de-ionizedwater in a 3000 ml stainless steel beaker. The stainless steel beakerwas placed in a constant temperature water bath and the CMC and waterwere mixed using an overhead air mixer. The CMC dispersion was heated toand maintained at a temperature of 80° C. in the water bath. Mixing wasfor one hour.

Then 100 g OD ML1 unbleached cellulose wood pulp fibers refined fibers(150 CSF) in 400 ml DI water were added to the stainless steel beakerand mixed with the CMC dispersion for 30 minutes. The temperature wasmaintained at 80° C. during mixing.

Then 12.0 g of 20% stock solution of polyDADMAC (2.4 g polyDADMAC)purchased from Sigma-Aldrich diluted with 500 ml of DI water was addedto the dispersion and mixing was continued for one hour. The temperaturewas maintained at 80° C. The fibers were filtered using a Buchnerfunnel/flask under water pump vacuum. The amount of polyDADMAC on thecellulose fibers was determined to be 1.78% of the weight of thecellulose fibers by Kjeldahl method of nitrogen determination.

5.0 g of the treated wet pulp fibers were added to 5000 ml DI water andmixed for 30 minutes using overhead mixing. The fibers were filteredusing a Buchner funnel/flask under water pump vacuum. The amount ofpolyDADMAC on the cellulose fibers was determined to be 1.58% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

Another 5.0 g of the treated wet pulp fibers was added to 5000 ml NaOHsolution (pH=12) and mixed for 30 minutes using overhead mixing. Thefibers were filtered using a Buchner funnel/flask under water pumpvacuum. The amount of polyDADMAC on the cellulose fibers was determinedto be 1.78% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

Experiment 9

Surface Treatment of Partially Bleached Cellulose Fibers.

Cellulose Fibers Treated in Water

1. with fibrillated CMC fibers (0.45 DS) (4% of cellulose fiber weight)and then

2. with polyDADMAC (100,000-200,000 Mw) (2.4% of cellulose fiberweight).

4.0 g (oven dry basis) of CMC (DS=0.45) was added to 1500 ml de-ionizedwater in a 3000 ml stainless steel beaker. The stainless steel beakerwas placed in a constant temperature water bath and the CMC and waterwere mixed using an overhead air mixer. The CMC dispersion was heated toand maintained at a temperature of 80° C. in the water bath. Mix was forone hour.

Then 100 g OD partially bleached cellulose wood pulp fibers in 400 ml DIwater was added to the dispersion in the stainless steel beaker andmixed for 30 minutes. The temperature was maintained at 80° C. duringmixing.

Then 12.0 g of 20% stock solution polyDADMAC (2.4 g polyDADMAC)purchased from Sigma-Aldrich diluted with 500 ml of DI water was addedto the dispersion in the beaker and mixed for one hour. The temperaturewas 80° C. The fibers were filtered using a Buchner funnel/flask underwater pump vacuum. The amount of polyDADMAC on the cellulose fibers wasdetermined to be 1.96% of the weight of the cellulose fibers by Kjeldahlmethod of nitrogen determination.

5.0 g of the treated wet pulp fibers was added to 5000 ml DI water andmixed for 30 minutes using overhead mixing. The fibers were filteredusing a Buchner funnel/flask under water pump vacuum. The amount ofpolyDADMAC on the cellulose fibers was determined to be 1.61% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

Another 5.0 g of the treated wet pulp fibers was added to 5000 ml NaOHsolution (pH=12) and mixed for 30 minutes using overhead mixing. Thefibers were filtered using a Buchner funnel/flask under water pumpvacuum. The amount of polyDADMAC on the cellulose fibers was determinedto be 1.96% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

Experiment 10

Surface Treatment of Partially Bleached Cellulose Fibers.

Cellulose Fibers Treated in Water

1. with fibrillated CMC fibers (0.27 DS) (4% of cellulose fiber weight)and then

2. with polyDADMAC (100,000-200,000 Mw) (2.4% of cellulose fiberweight).

4.0 g (oven dry basis) of CMC (DS=0.27) was added to 1500 ml de-ionizedwater in a 3000 ml stainless steel beaker. The stainless steel beakerwas placed in a constant temperature water bath and the CMC and waterwas mixed using an overhead air mixer. The CMC and water dispersion washeated to and maintained at a temperature of 80° C. in the water bath.Mixing was for one hour.

Then 100 g OD partially bleached cellulose wood pulp fibers in 400 ml DIwater was added to the CMC dispersion in the stainless steel beaker andmixed for 30 minutes. The temperature was maintained at 80° C. duringmixing.

Then 12.0 g of 20% stock solution polyDADMAC (2.4 g polyDADMAC)purchased from Sigma-Aldrich diluted with 500 ml of DI water was addedto the mixture in the beaker and mixed for one hour. The temperature wasmaintained at 80° C. during mixing. The fibers were filtered using aBuchner funnel/flask under water pump vacuum. The amount of polyDADMACon the cellulose fibers was determined to be 1.73% of the weight of thecellulose fibers by Kjeldahl method of nitrogen determination.

5.0 g of the treated wet pulp fibers were added to 5000 ml DI water andmixed for 30 minutes using overhead mixing. The fibers were filteredusing a Buchner funnel/flask under water pump vacuum. The amount ofpolyDADMAC on the cellulose fibers was determined to be 1.38% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

Another 5.0 g of the treated wet pulp fibers was added to 5000 ml NaOHsolution (pH=12) and mixed for 30 minutes using overhead mixing. Thefibers were filtered using a Buchner funnel/flask under water pumpvacuum. The amount of polyDADMAC on the cellulose fibers was determinedto be 1.61% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

Experiment 11

Surface Treatment of Partially Bleached Cellulose Fibers.

Cellulose Fibers Treated in Water

1. with fibrillated CMC fibers (0.38 DS) (4% of cellulose fiber weight)and then

2. with polyDADMAC (100,000-200,000 Mw) (2.4% of cellulose fiberweight).

4.0 g (oven dry basis) of CMC (DS=0.38) was added to 1500 ml de-ionizedwater in a 3000 ml stainless steel beaker. The stainless steel beakerwas placed in a constant temperature water bath and the CMC and waterwas mixed using an overhead air mixer. The CMC dispersion was heated toand maintained at a temperature of 80° C. in the water bath. Mix was forone hour.

Then 100 g OD partially bleached cellulose wood pulp fibers in 400 ml DIwater was added to the stainless steel beaker and mixed for 30 minutes.The temperature was maintained at 80° C. during mixing.

Then 12.0 g of 20% stock solution of polyDADMAC (2.4 g polyDADMAC)purchased from Sigma-Aldrich diluted with 500 ml of DI water was addedto the mixture in the beaker and mixed for one hour. The temperature wasmaintained at 80° C. The fibers were filtered using a Buchnerfunnel/flask under water pump vacuum. The amount of polyDADMAC on thecellulose fibers was determined to be 1.84% of the weight of thecellulose fibers by Kjeldahl method of nitrogen determination.

5.0 g of the treated wet pulp fibers was added to 5000 ml DI water andmixed for 30 minutes using overhead mixing. The fibers were filtered.The amount of polyDADMAC on the cellulose fibers was determined to be1.61% of the weight of the cellulose fibers by Kjeldahl method ofnitrogen determination.

Another 5.0 g of the treated wet pulp fibers were added to 5000 ml NaOHsolution (pH=12) and mixed for 30 minutes using overhead mixing. Thefibers were filtered. The amount of polyDADMAC on the cellulose fiberswas determined to be 1.73% of the weight of the cellulose fibers byKjeldahl method of nitrogen determination.

Experiment 12

Surface Treatment of Partially Delignified Catalytically CarboxylatedCellulose Fibers.

Catalytically Carboxylated Cellulose Fibers Treated in Water

1. with polyDADMAC (100,000-200,000 Mw) (2.4% of cellulose fiberweight).

2. Dispersed catalytically carboxylated partially delignified cellulosepulp fibers 50.0 g OD with a carboxyl level of 17.87 meq/100 g in 750 mlof de-ionized in a 3000 ml stainless steelbeaker. Placed the stainlesssteel beaker in a water bath and continued mixing with an overhead airmixer. The pulp slurry was maintained at a temperature of 55° C. in thewater bath.

Then polyDADMAC 6.0 g of 20% stock solution purchased from Sigma-Aldrichdiluted with 250 ml of DI water was added to the catalyticallycarboxylated fibers. After one hour mixing at 55 C, fibers were filteredusing a Buchner funnel/flask under water pump vacuum. The amount ofpolyDADMAC on the cellulose fibers was determined to be 1.97% of theweight of the cellulose fibers by Kjeldahl method of nitrogendetermination.

5.0 g OD wet pulp was then dispersed in 5000 ml (pH=12) NaOH solutionfor 30 minutes with overhead mixing. The fibers were filtered using aBuchner funnel/flask under water pump vacuum. The amount of polyDADMACon the cellulose fibers was determined to be 1.76% of the weight of thecellulose fibers by Kjeldahl method of nitrogen determination.

TABLE 2 polyDADMAC polyDADMAC (Aldrich) (Aldrich) Low DS CMC (MW =100,000- (MW = 100,000- (DS = 0.45) 200,000) 200,000) % applied %applied % retained Sample on fibers on fibers on fibers 1 15316-30 4%2.4% 1.76% 15316-30A (alkaline wash) 4% 2.4% 1.61% 15316-30B (pH = 6 DIwater wash) 4% 2.4% 1.38% 2 15316-31 4% 1.2% 0.77% 15316-31A (pH = 6 DIwater wash) 4% 1.2% 0.50% 15316-31B (alkaline wash) 4% 1.2% 0.50% 315316-36 2% 1.2% 0.68% 15316-36A (pH = 6 DI water wash) 2% 1.2% 0.58%15316-36B (alkaline wash) 2% 1.2% 0.54% 4 15316-37 2%  3% 1.15%15316-37A (pH = 6 DI water wash) 2%  3% 0.86% 15316-37B (alkaline wash)2%  3% 1.08% 5 15316-33 2% 2.4% 1.15% 15316-33A (pH = 6 DI water wash)2% 2.4% 0.87% 15316-33B (alkaline wash) 2% 2.4% 1.04% 6 15316-41 1%  3%1.10% 15316-41A (pH = 6 DI water wash) 1%  3% 0.76% 15316-41B (alkalinewash) 1%  3% 0.95% 7 15316-42 1% 2.4% 0.98% 15316-42A (pH = 6 DI waterwash) 1% 2.4% 0.76% 15316-42B (alkaline wash) 1% 2.4% 0.88% 8 4% 2.4%1.78% (pH = 6 DI water wash) 4% 2.4% 1.58% (alkaline wash) 4% 2.4% 1.78%9 4% 2.4% 1.96% (pH = 6 DI water wash) 4% 2.4% 1.61% (alkaline wash) 4%2.4% 1.96% 10 4% 2.4% 1.73% (pH = 6 DI water wash) 4% 2.4% 1.38%(alkaline wash) 4% 2.4% 1.61% 11 4% 2.4% 1.84% (pH = 6 DI water wash) 4%2.4% 1.61% (alkaline wash) 4% 2.4% 1.73%

What is claimed is:
 1. A naturally cured fiber-cement productcomprising: cement; a synthetic polymer fiber; and a treated cellulosewood pulp fiber, said pulp fiber being treated with a fibrillatedcarboxyalkyl cellulose having a degree of substitution lower than about0.45 and with a quaternary ammonium polymer.
 2. The fiber-cement productof claim 1, wherein the quaternary ammonium polymer ispoly(diallyldimethylammonium chloride).
 3. The fiber-cement product ofclaim 1, wherein the synthetic polymer fiber is one or more of apolypropylene fiber and a polyvinyl alcohol fiber.
 4. The fiber-cementproduct of claim 1, wherein the synthetic polymer fiber is present in anamount of about 1.5-3.0% by weight.
 5. The fiber-cement product of claim1, wherein the wood pulp fiber is present in an amount of about 1.0-5.0%by weight.
 6. A naturally cured fiber-cement product comprising cementand a treated cellulose wood pulp fiber, said fiber being treated with afibrillated carboxyalkyl cellulose having a degree of substitution lowerthan about 0.45 and with a quaternary ammonium polymer.
 7. Thefiber-cement product of claim 6, wherein the fibrillated carboxyalkylcellulose is present in the treated cellulose wood pulp fiber in anamount of about 1.0-4.0% by weight.
 8. The fiber-cement product of claim6, wherein the treated cellulose fiber has at least 2 meq/100 g of fiberof the quaternary ammonium polymer retained thereon.
 9. The fiber-cementproduct of claim 6, wherein the quaternary ammonium polymer ispoly(diallyldimethylammonium chloride).
 10. The fiber-cement product ofclaim 9, wherein the treated cellulose fiber has about 0.5-2.0% byweight of poly(diallyldimethylammonium chloride) retained thereon. 11.The fiber-cement product of claim 6, wherein the fibrillatedcarboxyalkyl cellulose is fibrillated carboxymethyl cellulose.
 12. Thefiber-cement product of claim 6, further comprising one or more of asynthetic polymer fiber and an untreated cellulose wood pulp fiber. 13.A method of preparing a fiber-cement product, the method comprising:adding fibrillated carboxyalkyl cellulose having a degree ofsubstitution lower than about 0.45 and a quaternary ammonium polymer tocellulose wood pulp fibers to produce a treated cellulose fiber havingquaternary ammonium polymer retained thereon; forming a fiber-cementproduct from the treated cellulose fiber and cement; and naturallycuring the formed fiber-cement product.
 14. The method of claim 13,further including, prior to adding fibrillated carboxyalkyl cellulose,fibrillating said carboxyalkyl cellulose.
 15. The method of claim 14,wherein fibrillating is performed using high shear mixing ofcarboxyalkyl cellulose in water.
 16. The method of claim 13, wherein thefibrillated carboxyalkyl cellulose is added in an amount of about0.1-10% by weight of the cellulose wood pulp fibers.
 17. The method ofclaim 13, wherein the quaternary ammonium polymer is added in an amountof at least 2 meq/100 g of the cellulose wood pulp fibers.
 18. Themethod of claim C, wherein the quaternary ammonium polymer ispoly(diallyldimethylammonium chloride).
 19. The method of claim 18,wherein the poly(diallyldimethylammonium chloride) is added in an amountof about 0.1-10% by weight of the cellulose wood pulp fibers.
 20. Themethod of claim 18, wherein the treated cellulose fiber has about0.5-2.0% by weight of poly(diallyldimethylammonium chloride) retainedthereon.